Although both PT810 MMU and PTP820G use -48VDC as a power input, but if you are using PTP810 AC/DC power adaptor for PTP820, one thing you do need realized is you need to rewire the power cable.
THe reason is PTP810 and PTP820 -48VDC input are reversed, you must rewire and make the right polarity. Luckily, The PTP 820G monitors the power supply for under-voltage and includes reverse polarity protection, so that if the positive (+) and negative (-) inputs are mixed up, the system remains shutdown.
Following is the picture of PTP820 -48VDC input:
Following is the picture of PTP810 MMU -48VDC input: